Silicone pressure sensitive adhesives are widely used in transdermal drug delivery, wound dressings, scar dressings, and other healthcare applications. These adhesives are typically a condensation product of silicate resin and polydimethylsiloxane (PDMS) fluid, or a reactive blend of vinyl- and hydride-containing PDMS and a silicate resin cured via hydrosilylation reaction (Dow Corning Literature, Silicone Pressure Sensitive Adhesives (2002)). These adhesives are biocompatible, gentle on the skin, and securely attach medical devices to the body when the environment is dry. However, under moist conditions such as during skin perspiration, the hydrophobic silicone adhesives lose their adhesion to skin, which can lead to the dressing detaching from the body prematurely.
There is a need to improve the adhesion of these adhesives to skin in the presence of moisture. Traditionally, adhesion under moist environment in skin adhesives have been accomplished by adding water absorbing fillers such as hydrocolloids to pressure sensitive adhesives. The hydrocolloid fillers absorb moisture and soften, providing wet tack, thereby improving the adhesion to skin longer. However, the disadvantages of this approach are the reduction in the dry peel strength and tack properties of the adhesive due to the presence of hard fillers. In addition, because of the affinity of the fillers for water, they dissolve and leach out of the adhesive, which can leave a slimy residue on the skin after the dressing removal.
In order to improve the adhesion of silicone adhesives under a moist environment and to overcome the drawbacks of previous approaches, the present approach is to add a suitable amphiphilic silicone copolymer to a silicone pressure sensitive adhesive. An ideal amphiphilic silicone copolymer suitable for such applications should possess high cohesive strength, high moisture vapor transmission rate (MVTR), high pressure sensitive adhesion to surfaces, maintain adhesion even under moist conditions, and should not leach out components or leave a residue. Commercially available amphiphilic silicone copolymers are typically based on grafted poly(ethylene glycol). These copolymers are low molecular weight liquids, which are typically used as surfactants or defoamers. Addition of such low molecular weight copolymers can affect the adhesive performance because of surface migration under moist conditions and lead to a reduction in adhesion.
Several amphiphilic silicone copolymers have been reported in the literature. Recently, G. Edrodi and J. P. Kennedy published the synthesis of amphiphilic conetworks of poly(ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) (G. Edrodi and J. P. Kennedy, J. Polym. Sci. Part A: Polym. Chem., 43, 4954-4963 (2005)). The amphiphilic conetworks exhibited swelling in water and hexane indicating bi-continuous phases.
Yildiz, et al. synthesized block copolymer of poly(vinyl pyrrolidone)-poly(dimethyl siloxane)-poly(vinyl pyrrolidone) (J. C. Kim, M. Song, S. Park, E. Lee, M. Rang, and H. Ahn, J. Appl. Polym. Sci., 85, 2244-2253 (2002)). They prepared a di-isocyanate terminated PDMS which was then end-capped with t-butyl peroxide. This was used as a macrointiator for N-vinyl pyrrolidone polymerization. The resulting copolymers showed lower glass transition temperature (Tg) than the homopolymer poly(vinyl pyrrolidone).
Graiver, et al. used aldehyde-functional silicones as reactive sites for vinyl copolymerization in the presence of a copper redox system (D. Graiver, G. T. Decker, Y. Kim, F. J. Hamilton, and H. J. Harwood, Silicon Chemistry, 1, 107-120 (2002)). Several graft and block copolymers including polymethacrylic acid and polyacrylic acid were incorporated into the silicone polymer. These polar segments were formed by the thermal decomposition of the t-butyl ester substituted polyacrylate segments.
Yilgor, et al. synthesized triblock copolymers of polycaprolactone-PDMS, and poly(2-ethyl-2-oxazoline)-PDMS (I. Yilgor, W. P. Steckle, E. Yilgor, R. G. Freelin, and J. S. Riffle, J. Polym. Sci. Part A: Polym. Chem., 27, 3673-3690 (1989)). For the caprolactone, hydroxyl-terminated PDMS was used as a macroinitiator, and for the oxazoline copolymers, benzyl chloride-terminated PDMS was used. The resulting copolymers with a silicone content of about 30-50% were shown to reduce the surface tension of plastics, such as PET, PMMA, and polyurethane.
Yildiz, et al. synthesized poly(N-isopropylacrylamide) hydrogels using diacrylate-terminated PDMS as the crosslinker (Y. Yildiz, N. Uyanik, and C. Erbil, J. Macromol. Sci., Part A: Pure and Applied Chemistry, 43, 1091-1106 (2006)). The resulting hydrogels were found to have higher compression moduli compared to the conventional crosslinker, N,N′-methylene bis-acrylamide. This was attributed to the hydrophobic interactions between PDMS segments in the network.